Carburetor



United States Patent CARBURETOR Elmer Olson, Rochester N. Y., assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Thisinvention relates to carburetors for internal combustion engines, particularl-yengines for automotive vehicles and more specifically to automatic choke mechanism operable to automatically control the position of an air inlet valve for the purpose of controlling the fuelairratio of themixture supplied to the engine.

Automatic choke devices operable to move a choke or air inlet valve to different positions in response to variations in engine temperature and/ or suction are commonly provided in carburetors at the present time. These devices generally include an unbalanced valve in the carburetor air inlet which is subject to pressures created by the air entering the carburetor, is also controlled by a thermostat which exerts a force to hold thevalve closed at low temperatures and also by a suction operated member connected to the valve and responsive to variations in suction posterior to the throttle, which exerts a force tending to open the valve as such suction increases.

.-In some installations conventional automatic choke devices now in use are not wholly satisfactory to produce a mixture of the desired fuel-air ratio throughout the entire range of movement of the choke valvefromits fully closed to fully open position. 'For example, the mixture maybe somewhattoo rich in one partof the choke valves movement and too lean in another part to meet the exact mixture requirements for some particular installation. In our particular installation it has been observed that with the usual conventional automatic choke device, the mixture during the first partof the opening movement of the choke valve, for example, the first twenty-five degrees thereof, the mixture provided by the carburetor was too rich for wholly satisfactory engine operation, but during :the remainder of the travel of the choke valve a mixture of correct portions was supplied. -It is, therefore, the principal purpose of the present invention to provide a carburetor havingautomaticchoke mechanism in which novel means is provided which is effective to increase the rate of movement of the choke valve toward open position, for any given increase intemperature, during the first part of the opening movement of the choke valve, but which becomes ineffective ,after the choke valve reaches a predetermined open position.

According to the present invention, a spring is provided which urges the choke valve toward open position and which opposes the closing force of the'thermostat but which becomes entirely ineffective to exert any force whatever on the choke valve after the latter has made a predetermined opening movement. The force exerted by this spring must be, of course, less than the closing force exerted by the thermostat.

Further objects and advantages of the present invention will'be apparent from the following description, reference being had to the accompanying drawings wherein a preferred embodiment of thepresent invention is clearly shown.

In the drawings:

Figure 1 is a vertical section, partly in elevation, ofa carburetor in which the present invention is embodied;

Ratented Dec. 31, 1957 Figure 2 is an enlarged detail section on the line,2-2 of Figure 1;

Figure 3 is a horizontal detail section on the line .3..3 of Figure 2;

Figure 4 is a detail section on the line 4-4 of Figure 2; and

Figure 5 is a fragmentary detail view of .a modified form of the invention.

The carburetor as shown herein comprises three castings, 2, 4 and 6, suitably secured together by screws 8, or in any suitable way. The casting 2 is the air inlet casting having a passage 10 for admission ofair. The casting 4 is the fuel chamber casting and has a constant level fuel chamber 12 therein, in which fuel is maintained at a substantially constant level by mechanism which will be very briefly described later. The passage 10 communicates with a chamber or passage 14 centrally located in the casting 4 into which fuel is introduced and which forms the mixing chamber of the carburetor.

The casting 4 is immediately above and secured to the casting 6, which is the outlet casting, and is secured in any suitable way to the intake manifold of the engine. An outlet passage 16 is formed in the casting 6 and connects with the passage 14, the passages 10, 14 and '16, forming a continuous intakepassage through the carburetor through which air entering the inlet flows and is mixed with fuel to form a combustible mixture which flows through the outlet passage 16 to the engine.

The flow of mixture'from the carburetor is controlled by a suitable throttle valve 18 secured to a shaft 20 suitably journalled for rotation in --the walls of casting 6. This throttle is manually operated in the usual manner by means of an arm 22 secured to one end of the shaft 20 and is variably positioned to control the volume of mixture supplied to the engine and the speed thereof.

Fuel is supplied to the fuel chamber 12 through a passage 24 formed in the wall of casting 2 and communicating with this passage is a nipple 26 threaded in the wall of casting 2 and'having a passage 28 which conveys fuel from passage 24 to chamber 12. The nipple '26 is enlarged at its lower end to form a cylindrical chamber 30 in which is received a valve 32 which controls flow through passage 23. This valve is freely movable and its lowerend rests on a tank 34 cut out from and integral with a plate or bracket 36 which is secured :to a float, (not shown), and is pivoted on a pin 38 mounted in lugs 40 which are integral with and depend from'the casting 2 into the'chamber l2. Whenthe fuel reaches a predetermined level, the float is raised enoughto move the valve 32 against its seat to close passage 28. This is a conventional float valve construction and formsno part of the present invention.

A tube 42 is secured at its upper end in any suitablev way to an annular rib 4-4 projecting from the casting 2 and has a fuel passage 46 formed therein to convey fuel from thechamber 12 to the carburetor mixing chamber. A calibrated plug 48 is screwed into the lower end of tube 42 and meters the fuel supplied to the mixing chamber. The passage 46, at its upper end, connects with a crosspassage 50 formed in a bridge'member 52 Which extends across the mixing chamber and isintegral with the casting 2. The passage 50 supplies fuel to the main nozzle 54 which extends into a smallventuri tube 56 positioned in the mixing chamber and extending into a large venturi 57 which forms the wall of themixing chamber. A plug 58 having a restricted orifice therein is positioned in the main nozzle to aid in atomizing the fuel. Air is admitted to the passage 50 through two small passages 60 to mix with the fuel fiowingtherethrough.

Positionedin the bridge piece 52 atthe right of the mainnozzle is a sleeve 62 havinga passage therethrough for idling fuel and, at its rightendthis sleeve is somewhat,

gara es reduced in size so that it is spaced from the wall of the passage 50, as shown in Fig. l. The fuel which flows through the sleeve 62 ultimately reaches the passage 64 which supplies fuel to idling fuel supply inlets (not shown), which deliver fuel adjacent the edge of the throttle valve 18.

The admission of air to the passage is controlled by an automatically operated choke valve 79 secured to a shaft 72 suitably journalled for rotation in the wall of the casting 2. This shaft has secured on the left end thereof, as seen in Fig. 1, an arm '74 which has a horizontally extending portion 76. The shaft 72 extends into a housing 78 which is a part of casting 2 and is provided with a removable and adjustable cover-plate 811 which may be either metal or a suitable plastic and is held in any adjusted position by screws 82. The arm '76 on the end of the choke shaft and cooperating parts, about to be described, are positioned in this housing.

The arm 76 is engageable by the hooked end 8 1 of a thermostat 86, the other end of which is secured to a pin 88 which is fixed in the cover-plate 30, as shown in Fig. 1. Upon reduction of temperature, the hooked end 8-4 moves counter-clockwise, as seen in Fig. 2, to engage the extension 76 of arm 74 and exerts a pressure thereon to hold the choke valve in closed position, as shown in Fig. 2. By adjustment of plate 81 the pin 88 is rotated and changes the pressure exerted by the thermostat at any given temperature to hold the choke valve closed.

The lower end of the arm 74, as seen in Fig. 2, is pivorally connected to a link 90 which is pivotally connected to cross-pin 22 extending across a slot 93 in the right end of a piston 94 slidable in a horizontal cylinder 96 integral with the housing 78 and to which the suction maintained in the intake passage posterior to the throttle 18 is communicated through a passage 98. The passage 98 may connect with the carburetor outlet between the throttle and the manifold, or with the intake passage in the manifold itself. The particular position of this connection is not material as long as it is on the engine side of the throttle. Grooves 100 are formed in the wall of the cylinder 96 and these grooves are blocked by the piston when it is in its normal position, but when the engine starts to run under its own power the piston is pulled to the left enough to uncover the grooves. This efiects two results. First, it reduces the suction which is effective on the piston because of the passage of air through the grooves and, second, the grooves communicate the suction to the thermostat housing 78 and this suction is effective to draw heated air through the housing, such air beingadrnitted through the passage 102 which is connected by any suitable coupling to a conduit 104 leading to the conventional exhaust stove.

The thermostat tends to move the valve counterclockwise. as seen in Fig. 2, and is effective to hold the valve 711 closed at temperatures lower than room temperature with a force that varies inversely with the temperature. The suction communicated to the cylinder 96 which is effective on the piston 94 and the pressure differential across the unbalanced valve 70 itself, both oppose the force of the thermostat and when these forces overcome the force of the thermostat, the valve will be moved toward open position. During cranking of the engine by the starting motor, when the engine is being started, such forces are insufiicient to overcome the force of the thermostat and the valve 70 remains closed, but as soon as the engine begins to run under its own power, the valve moves toward open position until it reaches a position where the closing force of the thermostat is balanced by the forces opposing it. If course, as the engine continues to run and the temperature of the engine increases, the closing force of the thermostat will be reduced while the forces opposing such closing force may increase or remain the same, depending on the position of the throttle and engine speed. In any event, after the engine starts and runs under its own power, the valve '70 is progressively opened until it reaches fully open position when normal engine temperature is reached.

In order that the first part of the opening movement of the choke valve shall be greater for any given increase in temperature than the last part of the valves movement, a spring 1% is provided which aids the effect of suction, on the piston and on the valve itself, to open the valve during a part only of the valve movement. Obviously, this spring opposes the force of the thermostat, but exerts force less than that of the thermostat. The arm 74 fits on a flattened extension 1% of the shaft 72 and a retaining member provided with a hub portion 112 fits on the extension 108 outside the arm 74, the end of the extension being riveted over the member 110 to hold the parts in assembled position as indicated in Fig. 4.

The spring 106 is a torsion spring which has a number of coils surrounding the hub 112 and one end 114 of such spring extends to the right, as seen in Fig. 2, to engage the underside of a pin 116 extending from the wall of the housing 78 while the opposite end 118 of the spring engages the upper side of a short arm 120 extending laterally from the arm 74, as shown in Fig. 2. Obviously, this spring pushes downwardly on the arm 120, tending to open the valve against the force of the thermostat. The spring is so constructed that it ceases to exert any force on the arm 121) after the valve has made a predetermined opening movement, for example, twenty-five degrees.

In Fig. 5 there is shown a modified form of the invention in which the spring, which opposes the closing action of the thermostat and associated mechanism, is at the opposite end of the choke valve shaft and outside the carburetor housing. In this figure of the drawings, the choke valve shaft is designated by the numeral and secured to the shaft is an arm 132 which has a laterally offset portion 134 provided for a purpose more fully set forth later.

The shaft 130 extends through and is rotatable in a boss 136 which projects from the main carburetor housing 138. Rotatably mounted on a hub which extends to the right from the arm 132 and surrounds the shaft 130 is an arm 140 which has a lateral extension 142 positioned immediately below the arm 132, as seen from the left in Fig. 5. At the opposite end of the arm 140 it has an opening through which extends a laterally offset portion 144 of a rod 146 which extends downwardly, as seen from the left in Fig. 5, to a fast idle stop which is positioned by the rod to increase the idling speed at low temperatures. The arrangement of this rod and idle stop forms no part of the present invention and maybe of the same construction as shown in the copending application of Olson et al., S. N. 264,136, filed December 29, 1951, now Patent No. 2,771,282, dated November 20, 1956. The lateral extension 144 of rod 146 which extends through the arm 140 is held in position by a washer 148 which engages a groove in the extension 144 or is held in position in any other suitable way.

Since the mechanism described above is at the opposite end of the choke valve shaft from that shown in Fig. 2, a clockwise movement of the shaft, as seen from the left in Fig. 5, would effect closing of the choke valve instead of a counter-clockwise movement, as in Fig. 2, and the thermostat at the opposite end of shaft 130 rotates such shaft clockwise upon decrease in temperature, and on increase in temperature the thermostat would permit counter-clockwise movement of the shaft 130 to effect opening of the choke valve. On clockwise movement of the choke valve to its closed position, the arm 132 engages the extension 142 of arm 140, thus moving arm 140 clockwise and lifting the rod 146, as seen from the left in Fig. 5. This, of course, occurs at low temperatures and the rod 146 positions the idle stop (not shown), to increase the idle speed. As the temperature increases, the arm 140 is permitted to move in a counter-clockwise direction, moving the idle stop in a direction to progressively decrease the idle speed until, when normal operating speed is reached, the idle speed will be at a minimum.

Surrounding the boss 136 is a torsion spring 150 having crossed linear end portions and which spring performs the same function as the spring 106. One linear end portion 152 of this spring, as seen from the left in Fig. 5, engages the upper side of a pin 154 which extends from the housing 138, to which it is secured in any suitable way. The other end 156 of the spring 150, not only lies below the pin 154 but also below and in engagement with the lateral extension or projection 134 of arm 132, as seen from the left in Fig. 5, to oppose clockwise movement of the valve by the thermostat, upon decrease in temperature. In other words, the thermostat, although exerting more force on the valve to effect closing thereof than the force which can be exerted by the spring 150, is opposed by such spring and when the temperature increases, the spring tends to open the valve during a part of its opening movement, just as the spring does in the device shown in Fig. 2.

After the valve is opened to a predetermined extent, 20 for example, the spring 150 ceases to be efiective. When the choke valve is opened to the desired extent, the end 156 of the spring strikes the under side of pin 154 and further movement of such end of the spring is prevented. When this takes place, the spring no longer exerts any force tending to move arm 132 in a clockwise direction, as seen in Fig. 5, so that opening of the choke beyond the predetermined position referred to is not influenced in any way by the spring 150. The function of the device of Fig. 5 is substantially the same as that of Fig. 2.

While the embodiment of the present invention as herein disclosed constitutes a preferred form, it is to be understood that other forrns might be adopted.

What is claimed is as follows:

1. A carburetor having a mixture passage adapted to supply a mixture of fuel and air to an internal combustion engine, a fuel supply chamber for supplying fuel to said mixture passage, fuel and air inlets for said mixture passage, a choke valve mounted on a shaft for controlling the admission of air through said inlet, an operating arm connected to said valve, a thermostat operable to move said valve to closed position at low temperatures and to move said arm, a suction operated piston operable to move said valve toward open position upon increase in suction effective on said piston, a spring mounted on the choke shaft and having one end adapted to engage said arm, a fixed stop mounted on said carburetor adjacent said arm, the other end of said spring being adapted to engage said stop only during the final choke closing movement of said arm by said thermostat, the final choke closing movement of said arm moving the associated end of said spring into engagement with the fixed stop engaging end to progressively increase the resistance of said spring to the thermostat closing force.

2. A carburetor having a mixture passage adapted to supply a mixture of fuel and air to an internal combustion engine, a fuel supply chamber for supplying fuel to said mixture passage, fuel and air inlets for said mixture passage, a choke valve mounted on a shaft for controlling the admission of air through said inlet, an operating arm connected to said valve, a thermostat operable to move said valve to closed position at low temperatures and to move said arm, a suction operated piston operable to move said valve toward open position upon increase in suction effective on said piston, a spring coiled about said choke shaft and terminating in a pair of linear portions, a fixed stop mounted on said carburetor proximate said arm, said linear spring portions respectively operatively engaging said arm and said stop during the final closing movement only of said choke valve to charge said spring and thereby provide an initial choke opening force actuating in opposition to the thermostat closing force.

3. A carburetor having a mixture passage adapted to supply a mixture of fuel and air to an internal combustion engine, a fuel supply chamber for supplying fuel to said mixture passage, fuel and air inlets for said mixture passage, a choke valve mounted on a shaft for controlling the admission of air through said inlet, an operating arm connected to said valve, a thermostat operable to move said valve to closed position at low temperatures and to move said arm, a suction operated piston operable to move said valve toward open position upon increase in suction effective on said piston, a spring coiled about said choke shaft and terminating in a pair of crossed linear portions, a fixed stop mounted on said carburetor adjacent said choke shaft and engageable by one of said spring portions during the final closing movement of said valve, a projection formed on said arm proximate said stop and engageable by the other linear spring portion whereby the final valve closing movement charges said spring enabling the latter to work said valve open to a limited extent against the closing force of said thermostat.

References Cited in the file of this patent UNITED STATES PATENTS 2,124,778 Hunt July 26, 1938 2,408,104 Stanton Sept. 24, 1946 2,427,030 Swigert Sept. 9, 1947 

